This invention relates generally to switch apparatus, and more particularly to a switch apparatus suitable for use in an automotive vehicle to serve various functions including the function of commanding, setting and releasing of a constant-speed running control unit.
In a switch apparatus generally provided in an automotive vehicle, a horn switch only is disposed on an upper part of the steering wheel, while some of the others are mounted on the steering column, and the remaining ones are disposed on the instrument panel. However, it is desirable that such switches as those, which are provided for the purpose of controlling the constant-speed running control unit and which should be manipulated while the vehicle is being driven, be located so as to be readily manipulated by the hand of the driver who grips the steering wheel, and it is also desirable that such switches be located at a position which permits instantaneous identification by the driver.
Due to, however, the fact that the steering wheel is mounted so as to be freely rotatable relative to the body of the vehicle, it is not easy to mount such additional switches on the steering wheel. In the case of the horn switch referred to above, a DC signal path including, for example, a conductor ring and a brush engaging therewith is provided so that the horn switch disposed on the upper part of the steering wheel can be electrically connected to the horn mounted on the vehicle body. However, provision of such a DC signal path for each of the individual switches to be additionally mounted on the steering wheel results inevitably in a complexity of the structure of the switch apparatus and results also in an undesirable reduction of the reliability of the switch apparatus.
A switch apparatus which obviates such disadvantages is disclosed in, for example, Japanese Patent Publication No. 41527/77. According to the proposal of this patent, the switch apparatus includes a single DC signal path and a signal voltage generator capable of generating a plurality of signal voltages different from one another in response to the manipulation of a plurality of switches respectively, so that each of the signal voltages can be transmitted by way of the single DC signal path. The proposed switch apparatus is, however, defective in that a disturbance such as a variation of the output voltage of the battery mounted in the vehicle or a voltage drop occurring at the conductor ring or any other parts tends to give rise to difficulty of accurately identifying the signal voltages corresponding to the individual switches.